Jesse Eisenberg in New York City, wearing a shirt by Tommy Hilfiger and pants and a tie by Polo Ralph Lauren.

Who invented Facebook? It's one of the great business disputes, brought to the screen this month by director David Fincher and writer-producer Aaron Sorkin in The Social Network. New York—based actor Jesse Eisenberg stars as Mark Zuckerberg, the computer prodigy who pulled ahead with the idea for the site at Harvard University in 2004. A few months earlier, though, Zuckerberg had been hired by three entrepreneurial students hoping to implement their vision of a “Harvard Connection” site, one that would merge the personal data of students in some of the same ways as Facebook would soon do. He took the job with the trio, which included a set of identical twins who rowed crew in the Olympics, but you don't hear their names around town. Zuckerberg, on the other hand, is now worth about $4 billion.

Zuckerberg is described by friends as quiet and gentle, but possessed of deeply antisocial tendencies. Eisenberg, 27, can relate: he becomes excessively nervous in large groups, does not own a TV, and never goes to the movies—nor does he have a Facebook page. He isn't sure who should have won the lawsuit between the threesome and Zuckerberg, which was settled for $65 million in 2008. “It would be irresponsible for me to speak to his influence on the company, because I don't know what happened,” says Eisenberg. “But as an actor, I had to believe that there was no one other than Mark who could have had the social insight, technical wherewithal, and, most significantly, the ambition to make Facebook work.”